Conducti vi ty changes resulting when sing.le crystal silicon is
cleaved in ultrahigh vacuum have been measured parallel to the cleavage
plane over various temperature ranges for gold dope~ and high.resistivity
boron doped silicon. The resulting change of conductivity is
related to the difference between the valence band edge and the Fermi
level in the bulk and at the surface, and to the quantity of charge
in the surface states which has been trapped from the bulk. Analysis
of the data shows a high density of surface states on the clean cleaved
surface, centered 0.28 ± 0.08 eV above the valence band edge. The den-
13 -2 -1
sity~depends on the model chosen, but is at least 10 cm eV •
Results obtained in this experiment are correlated with results obtained
by other experiments.
Oxygen absorption is observed to introduce different surface states,
also of high density but centered 0.6 + 0.15 eV above the valence band
edge of the surface. Low temperature measurements on gold doped silicon
crystals show that probably no conduction takes place through the surface
states themselves, either on clean or oxidized surfaces. These results
are used to obtain possible models of the surface state distributions.
A two dimensional conformal mapping is used to derive relations
between conductance change and conductivity per square for several
geometries, and to obtain corrections to the observed conductance change
f.or cleavage planes not parallel to the initial current flow lines.